There are three main types of antiperspirant stick formulations: compressed powder sticks, gel sticks, and wax sticks. While each of these formulation types may have advantages in certain usage situations, each also has disadvantages. For example, compressed powder sticks are often brittle and hard, leaving a cosmetically-unacceptable powder on the skin upon application. Wax-based formulations can also yield cosmetically-unacceptable products due to such factors as hardness, greasiness, and stickiness. The opacity of such wax sticks and the residue created by their use may also be aesthetically undesirable.
Gel-based sticks have several advantages over both compressed powder and wax sticks. For example, the gel sticks tend to leave little or no residue or dust on the skin. Gel sticks also provide a vehicle which glides easily over the skin's surface resulting in very easy and comfortable application of the product.
Unfortunately, the formulation of antiperspirant compositions in the form of effective and stable gel sticks is difficult. One critical ingredient in antiperspirant gel sticks is the gelling agent. Many known cosmetic gel sticks comprise gelled alcoholic solutions. Gelling agents, such as sodium stearate, have been used to form the gel. However, such gelling agents cannot be used in the presence of acidic antiperspirant active salts, due to interactions with the antiperspirant active.
Gelling agents which are more useful in the preparation of antiperspirant gel sticks are the dibenzylidene alditols, such as dibenzylidene sorbitol (DBS). See, for example, U.S. Pat. Nos. 4,154,816, Roehl et al., issued May 15, 1979; 4,816,261, Luebbe et al., issued Mar. 28, 1989; and 4,743,444, McCall, issued May 10, 1988. Various substituted dibenzylidene alditol gelling agents can also be used in antiperspirant gel sticks.
Japanese Published Application 64-62377, Kao, published Mar. 8, 1989, describes fluorinated dibenzylidene polyhydric alcohol derivatives which are effective gelling agents for cosmetic compositions containing a wide range of organic solvents.
U.S. Pat. No. 4,429,140, Murai et al., issued Jan. 31, 1984, discloses a method for producing DBS and its derivatives. Disclosed DBS derivatives include those where the benzene ring is substituted with from 1 to 3 lower alkyl groups, lower alkoxy groups, halogen atoms or nitro groups.
U.S. Pat. No. 4,371,645, Mahaffey, issued Feb. 1, 1983, describes plastic compositions which include DBS derivatives for improved transparency. These DBS derivatives must include a chlorine or bromine substituent in the meta and/or para positions and may also include lower alkyl, hydroxy, methoxy, mono- or dialkyl amino, or fluorine substituents. Di (para-chloro) DBS, di(para-fluoro) DBS, and di(para-methoxy) DBS are all specifically disclosed.
European Pat. Application 0286522, Roquette Freres, published Dec. 1, 1988, describes a process for making high purity alditol diacetals. Para-chloro DBS is disclosed.
Gelling agents found to be particularly useful for antiperspirant gel sticks are disclosed in U.S. Pat. No. application Ser. No. 07/505,807, Oh, Juneja, and Connor, filed Apr. 6, 1990. This application discloses substituted dibenzylidene alditols that are derivatized at the meta position of the benzene rings. Exemplary compounds include di (meta-fluoro) DBS and di(meta-chloro) DBS. These meta-substituted dibenzylidene alditols have improved stability in acidic conditions.
During processing and manufacture of antiperspirant gel sticks containing dibenzylidene alditol gelling agents, it is necessary to solubilize the gelling agent in a solvent, typically a monohydric or polyhydric alcohol. In order to do this, it is necessary to heat the ingredients to a temperature which is high enough to induce solubilization and which is also above the gel point of the gelling agent/solvent solution. Unfortunately, the relatively high temperatures required tend to cause the gelling agents to degrade in the presence of antiperspirant actives or other acidic materials. This is often exascerbated by practical matters during processing which often require that the composition be held at such high temperature, above the gel point, before packaging, and consequently cooling to form the gel, can be completed. Degradation can continue even at lower temperatures, throughout the life of the product. Accordingly, there is a need to provide antiperspirant gel stick compositions containing benzylidene alditol gelling agents which can exhibit improved gel stability. There is further a need to provide a process for making antiperspirant gel stick compositions by which decomposition of the gelling agent in the presence of acidic materials can be reduced.
It has been attempted in the past to meet these objects. For example, in U.S. Pat. Nos. 4,722,835, Schamper et al., issued Feb. 2, 1988, 4,719,102, issued Jan. 12, 1988, Randhawa et al., 4,518,582, Schamper et al., issued May 21, 1985, and 4,725,430, Schamper et al., issued Feb. 16, 1988 it is proposed in specific compositions to incorporate certain basic metallic salts as stabilizing agents into antiperspirant sticks utilizing a dibenzylidene monosorbitol acetal gelling agent. The basic metallic salt added as a gelling agent stabilizing agents include magnesium sulfate, zinc acetate, zinc oxide, calcium acetate, magnesium oxide, calcium carbonate, calcium hydroxide, magnesium carbonate, sodium carbonate, zinc and potassium carbonate. U.S. Pat. No. 4,518,582 also discloses the use of hexamethylenetetramine as a gel stabilizer and 4,725,430 also discloses an N-(2-hydroxyethyl) acetamide. Whereas these compositions are said to have increased gelling agent stability, the stabilizers disclosed have certain disadvantages which limit their effectiveness or ability to be incorporated into viable consumer products, such as off-odors, compatibility with other ingredients (especially at acidic pH) , compatibility with the skin, etc.
The present invention provides specific gelling agent stabilizers to be used in dibenzylidene alditol-containing antiperspirant gel compositions which can provide improved gelling agent efficiency, improved gel stability of the composition, and reduced gelling agent interaction with acidic materials, e.g., antiperspirant active, in processing and storage. Additionally, the gelling agent stabilizers do not impart undesirable off-odors to the product and are compatible with other ingredients in the composition. The present invention also provides a method of making such compositions.